1. Field of the Invention
The present invention relates to a rotor having a dividable core for an electric motor, and a production method thereof.
2. Description of the Related Art
Generally, a rotor of an electric motor has a core which is constituted by stacking magnetic steel sheets, punched into an annular shape, in a direction of a rotation axis thereof. However, in some production methods of an (in particular, large) electric motor, in order to effectively use the magnetic steel sheets, a stator and/or the core of the rotor are not punched into an annular shape, instead, are punched into a plurality of members which are divided in a circumferential direction of the annular shape, and then the plurality of members are connected so as to form the annular shape.
For example, Japanese Unexamined Patent Publication (Kokai) No. 2000-116074 discloses a stacking mold device and a stacking method for a core member. Concretely, paragraph [0004] and FIG. 17 of this document describes that a first core member 4 is formed by aligning a plurality of core pieces 3 in a band shape, and core pieces 3 similar to the core pieces of first core member 4 are aligned in a band shape on first core member 4 so as to form a second core member 5 so that the first and second core members are symmetric in the longitudinal direction. These procedures are repeated so that edge portions 3a of core pieces 3 of first and second core members 4 and 5 are overlapped with each other, and edge portions 3a are rotatably coupled to each other by means of a pin member 6.
On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 2002-262496 discloses a core structure of a rotary electric machine. Concretely, paragraph [0014] of this document describes that “a divided core 1 is formed by dividing a rotor core of a rotary electric machine into four sector shapes. On circumferential edge surfaces of divided sector core 1, key-shaped convex and concave features 2a and 2b are formed. In divided core 1, a slit 3 for inserting a magnet, and a dowel 4 for alignment used when stacking the cores, are formed. Key-shaped convex and concave features 2a and 2b may be fitted to each other as shown in FIG. 2, and a circular plate may be formed by combining four divided cores 1.”
When a core is dividable as described in Japanese Unexamined Patent Publication (Kokai) No. 2000-116074 or Japanese Unexamined Patent Publication (Kokai) No. 2002-262496, magnetic steel sheet may be effectively used, on the other hand, production man-hours are increased due to a large number of components. When fitting (connecting) each component constituting the dividable core, a gap between each component may be uneven, a distance between poles may also be uneven, and therefore the electric motor may not be smoothly driven. When the fitting gap is eliminated, workability of the core is usually deteriorated, whereby the production man-hours are further increased. Therefore, in a rotor or stator using a dividable core, it is desired that (i) the core be easily produced (production man-hours are few) and that (ii) a gap between each component is even.
Further, when a dividable core is used for a rapidly rotating rotor, the rotor is often mechanically reinforced so that the rotor may have resistance to a centrifugal force when rotating, as well as a reaction torque. Therefore, while the number of components is increased by using a reinforcing member, the above points (i) and (ii) are still desirable.